The Millen 90281 High Voltage Power Supply has a DC output of 700 volts at a maximum
current of 250mA and a 6.3 VAC 4A filament voltage. Designed as a general purpose
power supply it is an excellent power source for both the 90800 and 90801 transmitters
HV and filament requirements.

The power supply uses two 816 mercury vapor rectifier tubes and has a two section
pi filter with 10 henry General Electric chokes and a 2-2-10 mfd bank of 1000 volt
General Electric Pyranol capacitors. All this power results in a one heavy power
supply! When used to power my 90801 transmitter I also require another DC low voltage
homebuilt supply to provide power for the oscillator/multiplier stage.

The first picture shows only the front control plate area as the remaining panel
is blank rack panel. In the rear picture notice the size of the 10 henry chokes,
on the upper left, in comparision to the 816 rectifiers.

Later versions of the 90281 had the capability of high/low voltage adjustment of
the DC output. This is done through the switch located above the fuse holder and
the terminal strip labeled LOW HIGH on the rear panel. Early version units do not
have these items. The switch places a 5 ohm 25 watt resistor in the primary of the
HV transformer for low voltage output. The jumper on the LOW HIGH terminal strip
will either insert or remove the input filter capacitor from the circuit. Removing
the input capacitor (LOW jumpered) changes the filtering configuration to a choke
input type. Thus voltage regulation is improved, but output voltage is reduced.
For early version units this same filter change is possible, but the unit must be
opened and the input capacitance disconnected.

The Remote Switch terminals (both versions) allow the connection of remote switches
which parallel the front panel filament and plate switches. The terminals can also
function as a remote means for controlling an external antenna relay. The later
is discussed in the article a Millen
Station Setup Guide.